(a) Field of the Invention
The present invention relates to a resource allocation processor and a method thereof. More specifically, the present invention relates to a processor for adaptive resource allocation for a multi-channel communication system and a method thereof.
(b) Description of the Related Art
Recently, the increase of the importance of image and data transmissions has created a demand for high-speed data transmission. Frequency resources are relevantly lacking, however, and therefore effective frequency use is necessary.
In a conventional orthogonal frequency division multiplexing (OFDM) system, a fixed modulating method is used or a modulating method is determined in consideration of average signal to noise ratios (SNR) for respective users. In addition, it is important to separately determine the modulating method because various SNRs are provided for respective subchannels in the OFDM system.
As a prior art, the “Ensemble Modem structure for imperfect transmission media” is disclosed in U.S. Pat. No. 5,054,034, filed on Oct. 1, 1991, wherein bits are differently allocated for the respective subchannels with reference to SNRs of the respective subchannels in a multi-carrier system, and therefore a maximum data transmission speed or a maximum performance gain is provided.
According to the U.S. Pat. No. 5,054,034, a ratio between a SNR for each subchannel and a SNR gap is computed. At this time, the SNR gap is determined by an error correction coding method or a desired bit error probability, and it represents a difference between a practical SNR and a desirable SNR to be required when a predetermined number of bits is transmitted. A number of subchannels to be used, k, is initialized to be 1, a maximum number of bits to be transmitted is intialized to be 0, and the recursive process is started. For a present number k, a number of bits to be transmitted to the respective subchannels is then computed, and the greatest number of bits is calculated. The process is repeatedly performed until k corresponds to a number of the subchannels, N, and a maximum value among the number of bit sums becomes a maximum number of bits. At this time, the number of bits is a final number of bits to be transmitted to the respective subchannels. A required power value is calculated by the final number of bits, the power is predetermined as a standard so as to establish a sum of the calculated values to be a desired value, and a subchannel allocation power is finally calculated. In this application, in order to adaptively allocate bits according to the SNRs for the respective subchannels in the OFDM method, the bits to be allocated to the subchannels are calculated increasing the number of usable subchannels with reference to SNR for each step, and therefore an optimal bit allocation is performed by using SNR in the OFDM method.
Also, in a paper entitled “Computationally Efficient Optimal Power Allocation Algorithms for Multi-carrier Communication Systems” by B. S. Krongold, disclosed in a journal, IEEE Trans. Commun, Vol. 1, pp. 23-27, 2000, a bisection method for solving modulating method determination and bit allocation problems is applied for the purpose of allocating with reference to SNR and determining a modulation method for each subchannel in the discrete multitone modulation (DMT) system. In the paper, when assuming that transmitter end is aware of channel information in the DMT system, the frequency resource is efficiently used by discriminating users according to the channel information in a frequency band.
According to the paper, it is difficult to directly find an optimal solution for a nonlinear optimization problem having an integer type of variable, and therefore the solution for the nonlinear optimization problem is found when integer conditions on variables are eliminated, and a final integer solution is found by quantizing the given real number solution. At this time, an optimal solution for the problem has not yet been provided because it is very complicated to find the solution for the optimization problem, and the integer solution is found by quantizing the given real number solution.
In addition, in a paper entitled “Increase in Capacity of Multiuser OFDM System using Dynamic Subchannel Allocation” by W. Rhee and J. M. Cioffiis, disclosed in the journal Proceedings of IEEE VTC', 2000, pp. 1085-1089, a subchannel to be allocated to each user is determined with reference to channel information in a multiuser OFDM method, an allocation power is then determined in the subchannel and therefore a problem is formulated establishing power for each subchannel and each user as a variable in order to maximize a total capacity, and an intuitional method for solving the problem is disclosed.
According to the paper, performance is expected to be reduced because the power is correspondingly distributed when the capacity for each user and each subchannel is computed. Although the capacity is maximized, the capacity is a real number value and an integer value is only used in a practically used modulation method. Accordingly, it is difficult to use the given value for a practical transmission.
A modulation method determination process is required to be performed for respective channels and time slots in order to adaptively allocate resources in the OFDM and a time division multiple access (TDMA). It is, however, difficult to practically realize in methods according to the prior art because it is very complex to perform the modulation method determination process.